Building a pipeline simply is an expensive undertaking. In Eastern Germany e.g. there's one built right now, the EUGAL-pipeline. It will be about 480 km long (check the English fact sheet) and, according to the governments response to a question by a member of parliament from May 2018 (in German only) those 480 km cost about 2,276 million Euro (see top of ...
The quantities of oil in a deposit are listed under two categories: resources and reserves.
Resources are deposits that could be converted to reserves if economic factors, prices and costs, were favorable.
Reserves are deposits that can be extracted for a profit.
What makes a deposit profitable involves many things:
The size of the deposit
The quality of ...
During glaciations, the shelves down to ~100m depth would have been above sea level, but they would have been covered by ice sheets.
The actual "ocean floor" would still be deep water.
There is a general explanation of the oil formation here and here, although they don't say when (or where the continents were when the sediments were deposited), ...